1. Technical Field
The disclosure relates to a liquid-sealed antivibration device.
2. Related Art
As an antivibration device such as an engine mount which supports a vibration source such as an automobile engine while preventing the transmission of vibrations of the vibration source to a vehicle body side, there has been known a liquid-sealed antivibration device having the following constitution. That is, the liquid-sealed antivibration device includes: a first mounting member to be mounted on a vibration source side; a second mounting member to be mounted on a support side; an antivibration base body which is interposed between the first mounting member and the second mounting member and is made of an elastomer; a main liquid chamber where the antivibration base body forms a part of a chamber wall; a sub liquid chamber where a diaphragm forms a part of the chamber wall; and an orifice flow passage which allows the main liquid chamber and the sub liquid chamber to be communicated with each other. Due to a liquid flow effect brought about by the orifice flow passage and a vibration control effect of the antivibration base body, the liquid-sealed antivibration device performs a vibration damping function and a vibration insulating function (see JP-A-2006-118547 and JP-A-2010-139023, for example).
In this type of liquid-sealed antivibration device, to cope with vibrations having frequencies in a wide range, there has been known a liquid-sealed antivibration device where a plurality of orifice flow passages tuned to different frequencies are provided therein, and these orifice flow passages are switchable. Particularly, the applicant of this application has proposed the structure disclosed in the International Publication WO2010/032344A1, the entire contents of which are incorporated herein by reference, aiming at the changeover of the orifice flow passages with the inexpensive structure.
That is, WO2010/032344A1 discloses the constitution where a valve member formed of an elastomeric membrane for opening and closing a second orifice flow passage is mounted on a partition body, an outer peripheral portion of the valve member is fixed to the partition body, an opening of the second orifice flow passage is closed by flexural deformation of a flexible membrane portion on an inner side of the outer peripheral portion due to the flow of a fluid in the second orifice flow passage, and the second orifice flow passage is opened in a state where the flexible membrane portion is spaced apart from the opening due to a communication hole formed in the flexible membrane portion. Due to such a constitution, the second orifice flow passage is not closed by the valve member with an input of relatively small amplitude and hence, properties which make use of the second orifice flow passage on a high frequency side can be realized. On the other hand, with an input of relatively large amplitude, the flow of the liquid in the second orifice flow passage is increased so that the valve member is subjected to flexural deformation whereby the second orifice flow passage on a high frequency side is closed. Accordingly, a high damping performance by a first orifice flow passage on a low frequency side can be ensured. Further, due to the structure where the second orifice flow passage is closed by the flexural deformation of the valve member formed of the elastomeric membrane, when the flow of fluid becomes small, the second orifice flow passage can be returned to an open state due to a restoring force which the valve member possesses. Accordingly, a biasing means such as a spring, a switching chamber for a negative pressure or the like is unnecessary so that properties can be switched at a low cost.
However, in the constitution described above, when an input of large amplitude is generated as in the case of traveling on a rough road, there exists a possibility that an impact absorbing ability of the valve member becomes insufficient. That is, in the valve member, a valve portion which closes the opening of the second orifice flow passage by flexural deformation is formed in a flat membrane shape and hence, there is almost no space for the further deformation of the valve portion after the second orifice flow passage is closed when the input of large amplitude is generated. Accordingly, kinetic energy of the valve member is hardly absorbed after closing the second orifice flow passage so that a large load is transmitted to the partition body thus giving rise to a possibility that abnormal sound is generated.
To prevent such abnormal sound generated in the inside of the liquid chamber from being transmitted to the inside of a cabin, for example, JP-A-2006-118547 discloses the structure where a connection rubber elastic body is interposed between a partition element body into which a movable plate is incorporated and an orifice member mounted on an outer periphery of the partition element body. Also JP-A-2010-139023 discloses the structure where a cap member which forms an air chamber between the cap member and a diaphragm is divided into a first portion and a second portion, and a rubber elastic connection portion is interposed between the first portion and the second portion. However, in the structure where the connection portion formed of the rubber elastic body is interposed in the midst of a vibration transmission path, the connection portion is separately incorporated into the structure thus pushing up a manufacturing cost. Further, due to the presence of the elastic body, a liquid pressure loss occurs thus giving rise to a possibility that properties are influenced due to lowering of a damping performance.